Lead frames are used to facilitate the mechanical mounting and electrical connection of electronic elements on a circuit board. A lead frame with integral connectors is produced by initially stamping out the lead frame from an elongate piece of tin-plated copper alloy. During stamping, terminal legs are stamped on the outer periphery of the lead frame and a "window" is stamped out of the center of the lead frame. The lead frame is then encapsulated in a thermoplastic material except for the portion of the lead frame connected to the lead wires (adjacent the terminal leg) . The lead frame is then cut between adjacent terminal legs to electrically isolate each lead wire and its associated terminal leg from other adjacent lead wires and their associated terminal legs. A circuit component is then mounted in the window and wire leads are attached between pads on the electrical element and the lead frame adjacent the desired terminal leg.
Typically, a wire is ultrasonically welded from the lead terminal on the lead frame to the desired pad on the circuit component. However, the lead wires cannot be ultrasonically welded to brass, copper or steel. Presently, the lead terminals of the lead frame are made with a strip of aluminum inlaid in the surface. The lead wires are then welded to the inlays. Because it is very difficult to plate aluminum, using an aluminum inlay is the only method feasible. However, the cost of inlaying aluminum into a strip of brass or copper is prohibitively high. Furthermore, the resulting weld to the inlaid aluminum is not as reliable as desired.
The present invention is directed to overcoming one or more of the problems discussed above.